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HOUSTON -- Insomnia was associated with a greater risk of developing depression, a 5-year longitudinal study showed.

Compared with "good sleepers," four insomnia trajectory groups in a Canadian cohort study all had a higher risk of depression at follow-up, with the greatest risk in those with progressive insomnia symptoms:

• Stable, low severity insomnia: RR 3.58 (1.87-6.84)
• Gradual improvement: RR 6.6 (3.09-14.10)
• Persistent symptoms: RR 15.15 (8.25-27.82)
• Progressive worsening: RR 19.77 (10.3-37.93)

"What these findings suggest is first, there is clearly evidence of distinct, long-term insomnia trajectories. And those trajectories of insomnia symptoms, particularly when they become a system or progressive, are associated with a significantly greater risk of developing depression," reported Charles Morin, PhD, of Laval University in Quebec City, Quebec.

"These findings underscore the importance of identifying and managing insomnia in a timely manner in order to prevent depression," he said at the annual SLEEP meeting, hosted jointly by the American Academy of Sleep Medicine and the Sleep Research Society.

Morin also explained that while, previously, insomnia has sometimes been somewhat trivialized, more recent research has added to the idea that "insomnia is not just a symptom of depression, it's actually a significant and independent risk factor for depression."

Both depression and issues surrounding adequate sleep are common, with insufficient sleep already identified as a possible risk factor for depression as well as a myriad of other health conditions.

Despite this, Morin highlighted a gap in the research on how exactly the two are connected. While there are meta-analyses supporting insomnia as a predictor of and , he noted that few take into account long-term trajectories of insomnia, at varying severity, and its subsequent impact on depression.

Morin stressed the bi-directional relationship between insomnia and depression, and how managing a patient's insomnia may be key to potentially mitigating the risk for developing depression.

For the present report, Morin's group conducted a secondary analysis of a Canadian population-based study that focused on the natural history of insomnia. Participants filled out annual surveys about sleep and health status for 5 consecutive years.

Those chosen for this analysis were people without depression at baseline who had available data on depression and insomnia status. Depression was defined as a score of 20 or more on Beck Depression Inventory-II (BDI-II) plus at least one core depression symptom, namely a positive score on items indicating sadness or a loss of pleasure or interest. Insomnia was tracked yearly through the Insomnia Severity Index.

A total of 2,725 participants were included in the final study analysis. Study participants were adults averaging 49.5 years old. The patient population was 60.9% female.

Participants were placed into five sleep categories: 23.9% were considered to be "good sleepers," 34.7% had low, but stable insomnia severity, 4.8% progressive worsening symptoms, 6.1% subthreshold insomnia cases with gradual improvements, and 30.5% persistent insomnia symptoms.

The main findings of the study remained fairly consistent on sensitivity analyses, including one removing the sleep item on the BDI-II.

Sensitivity analysis suggested that subthreshold cases of insomnia, alongside gradual improvements, did not confer a greater risk of depression development when compared with a low, stable form of insomnia.

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